The overall objective of the proposed research is to define the role of estrogen in the regulation of growth and function in the human uterus. We plan to accomplish this by utilizing the cell culture system recently perfected in our laboratory as an in vitro system for characterizing directly the effects of estrogen on human uterine cells, for comparing the character of response of human endometrial cells to natural and synthetic estrogens and antiestrogens of therapeutic and contraceptive importance, and for analyzing the effects of multiple hormones on modulation of uterine responsiveness to estrogen.